Photo-degrading resinous composition and shaped article manufactured therefrom

ABSTRACT

A photo-degrading resinous composition which comprises: 
     A. from 50 to 100% by weight of a copolymer composed of i 95.0 - 99.9 % by weight of a monomer selected from the group consisting of styrene and methyl methacrylate, (ii) 5.0 - 0.1% by weight of a diene monomer and (iii) up to 4.9% by weight of an unsaturated ketone having the formula ##EQU1## wherein R 1 , R 2  and R 3 , which may be the same or different, represent a hydrogen atom or a methyl or phenyl group, and 
     B. up to 50% by weight of a thermoplastic synthetic resin other than said copolymer.

This is a division of application Ser. No. 213,211, filed Dec. 28, 1971,now U.S. Pat. No. 3,295,269.

This invention relates to a photo-degrading resinous composition whichdeteriorates and disintegrates readily under sun light or ultra-violetrays, and to a shaped article manufactured therefrom.

In general, when synthetic resins are left to stand under influences ofnature, they are hardly deteriorated by efflorescing actions such asoxidation and ozonization or by putrefaction by microorganisms.Accordingly, synthetic resin shaped articles such as containers, bags,films, foams and the like still retain their original forms even afterthey became disused and discarded, making their disposal veryinconvenient and cumbersome. In the present "age of plastics", syntheticresin articles are utilized in any field of modern living, and disposalof such disused plastic articles is presently a social problem.

For instance, disused plastic articles are collected together with otherwastes from households and discarded rivers or fields or reclaimed landsor burnt out. These disused synthetic resin articles contained in greatquantity in wastes retain their original forms for a very long timewithout undergoing deterioration, even after other waste materialsinclusive of organic waste materials other than synthetic resin articleshave deteriorated and disintegrated. This phenomenon results in varioussocial problems such as industrial, sanitary and scenery-defilingtroubles.

If waste articles of synthetic resins are collected separately fromother waste articles and only synthetic resin articles are disposed ofin some way or other, it includes various difficulties. For instance,collection of such waste synthetic resin articles requires much laborand time. In case they are burnt out in incinerators, black smokes orpoisonous gases are inevitably generated. Further, some synthetic resinsgenerate high temperatures when they are burnt out, which results inextreme shortening of life of incinerators.

It is an object of this invention to provide a photo-degrading resinouscomposition which will deteriorate and disintegrate readily underinfluences of nature when it has disused and left outdoors and whichwill not bring about the above-mentioned troubles as to disposalthereof.

Another object of this invention is to provide a shaped articlemanufactured from such photo-degrading resinous composition.

In accordance with this invention there is provided a photodegradingresinous composition which comprises:

a. from 50 to 100 % by weight of a copolymer composed of (i) 95.0 -99.9% by weight of a monomer selected from the group consisting of styreneand methyl methacrylate, (ii) 5.0 - 0.1 % by weight of a diene monomerand (iii) up to 4.9 % by weight of an unsaturated ketone having theformula ##EQU2## wherein R₁, R₂ and R₃, which may be the same ordifferent, represent a hydrogen atom or a methyl or phenyl group, and

b. up to 50 % by weight of a thermoplastic synthetic resin other thansaid copolymer.

This invention has been achieved based on the finding that a copolymerof styrene or methyl methacrylate with a small proportion of a dienemonomer readily deteriorates and disintegrates under sun light andultra-violet rays and that when the copolymer is blended with otherthermoplastic synthetic resin, the strength of the blend is extremelyreduced under sun light and ultra-violet rays and it readily undergoesdeterioration and disintegration.

The copolymer to be used in this invention is characterized by a dienemonomer content of 0.1 - 5 % by weight, preferably 0.5 - 4 % by weight,especially preferably 1 - 3 % by weight, based on the copolymer weight.At such preferable diene monomer content the photo-degrading property ofthe copolymer is very conspicuous.

It has been known in the art that styrene or methyl methacrylate iscopolymerized with a diene monomer such as butadiene to form a copolymerthereof. However, the purpose of such conventional copolymerization isto obtain rubbery elastic materials composed of a styrene-butadienecopolymer or a methyl methacrylate-butadiene copolymer, and in theseelastic materials, in general, the butadiene content is at least 10 % byweight. Thus, a styrene-diene copolymer or methyl methacrylate-dienecopolymer having such a low diene monomer content of 0.1 - 5 % by weightas intended in this invention has not been taken into consideration.Unlike conventional styrene-butadiene and methyl methacrylate-butadienecopolymers, the copolymer of styrene or methyl methacrylate having sucha low diene monomer content does not exhibit at all rubbery elasticity,but it still retains excellent characteristics inherent to polystyreneor poly(methyl methacrylate) with respect to strength, rigidity,hardness, transparency, etc.

Such copolymer may readily be prepared by any of conventionalpolymerization processes, such as suspension polymerization process,emulsion polymerization process, bulk polymerization process, etc.

As the diene monomer to be copolymerized with styrene or methylmethacrylate in the preparation of the copolymer of this invention,there may be exemplified butadiene, isoprene, chloroprene,2,3-dichlorobutadiene and 2,3-dimethylbutadiene. Use of butadiene andisoprene is especially preferred.

In this invention, units derived from an unsaturated ketone having thefollowing formula: ##EQU3## in which R₁, R₂ and R₃, which may be thesame or different, represent a hydrogen atom or a methyl or phenylgroup, may be introduced as the third copolymeric units into theabove-mentioned copolymer of styrene or methyl methacrylate with a dienemonomer. It has been found that the introduction of such thirdcopolymeric units further improves the photo-degrading property of theresulting copolymer.

Specific examples of the unsaturated ketone include methyl vinyl ketone,phenyl vinyl ketone, phenyl propenyl ketone and benzalacetophenoe. Useof methyl vinyl ketone is especially preferred. Such unsaturated ketoneis incorporated in an amount of up to 4.9 % by weight, preferably 0.5 -4 % by weight, especially preferably 1 - 3 % by weight, based on thecopolymer weight.

In this invention, it is important that the total amount of the dienemonomer and unsaturated ketone monomer is up to 5 % by weight based onthe copolymer weight. By adjusting the total amount of the diene monomerand unsaturated ketone monomer within such range, the resultingcopolymer can be allowed to retain desirable characteristics inherent topolystyrene or poly(methyl methacrylate).

Even when the styrene-diene or methyl methacrylate-diene copolymer orthe styrene-diene-unsaturated ketone or methylmethacrylate-diene-unsaturated ketone copolymer is used singly in thisinvention, it is possible to provide a resinous composition having asatisfactory photo-degrading property. Further, it is also possible toblend such copolymers with other thermoplastic synthetic resins. Also inthis case, there can be obtained resinous compositions having anexcellent photo-degrading property.

The kind of other thermoplastic resin to be blended into the copolymerof this invention is not particularly critical, and any of thermoplasticresins customarily used in the art may be used. Especially preferableexamples of such thermoplastic resin are polystyrene, polyethylene, poly(methyl methacrylate), poly(vinyl chloride), etc. Especially whenpolystyrene is used, desired properties of polystyrene such as highstrength, rigidity, hardness and transparency are not hardly lost butare retained in the resulting composition, and it may similarly be usedin fields where polystyrene has heretofore been utilized. Accordingly,it is especially preferred to blend polystyrene into the copolymer ofthis invention.

It is important that such thermoplastic resin is incorporated into thecopolymer in such an amount that the photo-degrading property of thecopolymer is not damaged by the incorporation. The thermoplastic resinis blended in an amount of up to 50 % by weight, preferably less thanabout 30 % by weight, based on the weight of the resulting resinouscomposition.

The resinous blend of the copolymer of this invention with otherthermoplastic resin may be prepared by a method comprising mixing thecopolymer with a thermoplastic resin, and blending or melt-kneading themby suitable blending means such as a mixing roll, a Bumbury's mixer andan extrusion kneader to form a homogeneous composition. It is alsopossible to adopt a method comprising impregnating a monomeric mixtureof styrene or methyl methacrylate and a diene monomer with a suitablethermoplastic resin such as polystyrene or dissolving the thermoplasticresin into the monomeric mixture, and effecting the polymerization.

It will readily be understood that the resinous composition of thisinvention may contain, in addition to the above ingredients,conventional additives to resins according to need. For instance, heatstabilizers, lubricants, fillers, pigments, plasticizers, various highmolecular substances and other additives may be incorporated in thecomposition of this invention. Still further, ordinary foaming agentsfor resins or foamable substances may be incorporated into thecomposition of this invention according to need. As such substancestherey may be exemplified propane, butane, n-hexane, pentane,dichloro-difluoro-methane, azobisisobutyronitrile and azodicarbonamide.By incorporation of such substances, it is made possible to provide foamproducts having a multicellular structure.

The above-mentioned additives and foaming agents may be introduced intothe resinous composition of this invention by customary methods adoptedin the art. For instance, they may be incorporated directly in theresinous composition, or they may be incorporated into the copolymer orthermoplastic resin in advance, following which such copolymer andthermoplastic resin are blended together.

The resinous composition of this invention may readily be shaped into aphoto-degrading article such as plate, sheet, film, vessel, containerand tube by customary shaping means such as injection molder, extrusionmolder, calendar roll, inflation molder, molding press and castingmolder.

Thus there are provided a resinous composition having an excellentphoto-degrading property and a shaped article thereof. Thermoplasticresins usually used as plastics in various fields have a degree ofpolymerization ranging from about 800 to about 5000. For instance, inthe case of polystyrene, when the degree of polymerization is reduced toabout 500 or less, the resin becomes fragile and brittle and is readilybroken or disintegrated. The resinous composition of this invention isdeteriorated and disintegrated with reduction of the molecular weight,when it is exposed to sun light or ultra-violet rays. More specifically,when the resinous composition of this invention is left alone outdoorsfor a period of about one week to several months, usually 1 - 5 months,the resinous composition is deteriorated to such an extent that thespontaneous disintegration is allowed to occur in the composition.

Accordingly, the resinous composition and shaped article of thisinvention may be conveniently applied to thrownaway uses. For instance,they may be used for preparation of packing sheets, packing films,simple tablewares such as thrownaway plates, saucers and cups,agricultural films, and the like. When these articles are thrown awaytogether with other wastes, unlike conventional synthetic resinarticles, they do not defile or damage nature or environment, but theyare spontaneously deteriorated and disintegrated under influences of sunlight and ultra-violet rays. Accordingly, labor and time required forcollection and incineration can be omitted.

This invention will now be detailed by referring to Examples, but itmust be noted that the scope of the invention is not at all limited bythese Examples.

EXAMPLE 1

A mixture of 320 g of styrene with 0.05 g of butadiene and 0.06 g ofbenzoyl peroxide was charged into a 30-cc capacity glass ampoule, andthe ampoule was sealed. The polymerization was conducted by heating themixture at 90°C. for 15 hours. The resulting polymer was taken out ofthe ampoule and dissolved in benzene. Methanol was added to the solutionto precipitate the polymer, and the precipitate was recovered byfiltration, washed with methanol, and dried in vacuo at 50°C. for 24hours to obtain a copolymer of Run No. 1 indicated in Table 1.

Runs Nos. 2 - 5 were performed in the same manner as above by varyingthe amounts of styrene and butadiene to be copolymerized therewith, andthere was obtained copolymers of Runs Nos. 2 . 5 indicated in Table 1.

These styrene-butadiene copolymers (10 g each) were dissolvedrespectively into 100 g of toluene and the solutions were formed intofilms of 0.1 mm thickness by the casting process. The films weresubjected to irradiation of a 400 watt high pressure mercury lampdisposed 15 cm apart from the sample, and the change in the degree ofpolymerization brought about by conducting the irradiation for apredetermined period of time was examined.

For comparison, a film was prepared in the same manner as above frompolystyrene having an average degree of polymerization of 1130, and itwas subjected to irradiation in the same manner as above. The change inthe degree of polymerization was determined.

Results are shown in Table 1.

                                      Table 1                                     __________________________________________________________________________    Butadiene   Degree of                                                                           Degree of Polymerization                                    Content     Polymeri-                                                                           After Irradiation                                           Run No.                                                                             (wt. %)                                                                             zation                                                                              4 hours                                                                            8 hours                                                                            16 hours                                                                            32 hours                                    __________________________________________________________________________    1     0.21  1260  1103 991  820   663                                         2     0.83  1370  1070 875  748   536                                         3     1.91  1150  755  605  440   315                                         4     3.28  2380  1370 935  724   377                                         5     4.87  1070  640  455  414   302                                         6     0     1130  1105 1085 1050  910                                         (control)                                                                     __________________________________________________________________________

EXAMPLE 2

Styrene-isoprene copolymers were prepared in the same manner as inExample 1 by employing isoprene instead of butadiene as a comonomer tobe copolymerized with styrene, and these copolymers were formed intofilms and tested in the same manner as in Example 1. Results are shownin Table 2.

                                      Table 2                                     __________________________________________________________________________                         Degree of Polymerization                                 Isoprene   Degree of poly-                                                                         after Irradiation                                              Content                                                                            merization be-                                                                          after 15 hours'                                                                         after 40 hours'                                Run No.                                                                             (wt. %)                                                                            fore irradiation                                                                        irradiation                                                                             irradiation                                    __________________________________________________________________________    7     0.3  1340      1130      690                                            8     0.7  1650      1030      680                                            9     1.2  1730      990       510                                            10    2.0  1110      520       220                                            11    3.8  1130      370       210                                            12    4.8  1830      570       190                                            13    0    1130      1080      890                                            (control)                                                                     __________________________________________________________________________

EXAMPLE 3

Copolymers indicated in Table 3 were prepared in the same manner as inExample 1 by varying the amount and kind of the comonomer to becopolymerized with styrene, and they were formed into films and testedin the same manners as in Example 1. For comparison, polystyrene of adegree of polymerization of 1120 prepared by homopolymerization ofstyrene was similarly formed in a film and tested. Results are shown inTable 3.

                                      Table 3                                     __________________________________________________________________________                               Degree of Polymerization                           Copolymer        Degree of Poly-                                                                         after Irradiation                                        Composition                                                                              merization be-                                                                          16 hours'                                                                            32 hours'                                   Run No.                                                                             (weigh ratio)                                                                            fore irradiation                                                                        irradiation                                                                          irradiation                                 __________________________________________________________________________    14    styrene-butadiene                                                                        1040      435    --                                                (97.6 : 2.4)                                                            15    styrene-butadiene-                                                                       1030      237    --                                                methyl methacrylate                                                           (97.8 : 1.1 : 1.1)                                                      16    styrene-butadiene-                                                                       1750      --     320                                               benzalacetophenone                                                            (96.0 : 2.0 : 2.0)                                                      17    styrene-isoprene-                                                                        1440      340    --                                                phenyl vinyl ketone                                                           (96.0 : 2.0 : 2.0)                                                      18    polystyrene                                                                              1120      1010   --                                          (control)                                                                     __________________________________________________________________________

EXAMPLE 4

A mixture of 20 g of methyl methacrylate with 0.5 g of butadiene and 0.1g of benzoyl peroxide was charged into a 30-cc capacity glass ampoule,and the ampoule was sealed. The polymerization was accomplished byheating the mixture at 90°C. for 6 hours. The resulting polymer wastaken out of the ampoule and dissolved in methyl ethyl ketone. Methanolwas added to the solution to precipitate the polymer. The precipitatewas recovered by filtration, washed with methanol, and dried in vacuo at50°C. for 24 hours to obtain a copolymer of Run No. 19 of Table 4.

Copolymers of Runs Nos. 20 and 21 of Table 4 were prepared in the samemanner as above by changing the amount and kind of the monomer to becopolymerized with methyl methyacrylate. For comparison, poly(methylmethacrylate) having a degree of polymerization of 1560 was alsoprepared.

These polymers were formed into films and tested in the same manner asin Example 1. Results are shown in Table 4.

                                      Table 4                                     __________________________________________________________________________                            Degree of                                             Copolymer Composition (wt. %)                                                                         Poly-  Degree of Polymerization                       methyl              methyl                                                                            merization                                                                           after Irradiation                                    metha-                                                                              buta-                                                                             iso-                                                                              vinyl                                                                             before 20 hours'                                                                            50 hours'                               Run No.                                                                             crylate                                                                             diene                                                                             prene                                                                             ketone                                                                            Irradiation                                                                          irradiation                                                                          irradiation                             __________________________________________________________________________    19    97.8  2.2 --  --  1540   550    350                                     20    98.1  --  1.9 --  1710   660    320                                     21    97.5  2.0 --  0.5 2030   440    280                                     22    100   --  --  --  1560   1300   1170                                    (control)                                                                     __________________________________________________________________________

EXAMPLE 5

A mixture of 500 g of styrene, 1.5 g of butadiene, 1.5 g of benzoylperoxide and 0.15 g of tert-butylperoxy benzoate was put into a 2-litercapacity autoclave charged with 500 g of a 0.5 % aqueous solution ofpolyvinyl alcohol, and the autoclave was sealed. The atmosphere insidethe autoclave was replaced by nitrogen, and the temperature was elevatedunder agitation to initiate the polymerization. The mixture was heatedat 90°C. for 7 hours and at 110°C. for additional 2 hours. The reactionproduct was taken out of the autoclave, washed with water and dried. Theso recovered polymeric product was dissolved in benzene, and methanolwas added to the solution to precipitate a polymer. The precipitate wasrecovered by filtration, washed with methanol and dried in vacuo at50°C. for 24 hours to obtain a styrene-butadiene copolymer having abutadiene content of 0.25 % by weight and an average degree ofpolymerization of 1150.

Then, 9.5 g of the so obtained styrene-butadiene copolymer and 0.5 g ofpolystyrene having an average degree of polymerization of 1130 wereadded to 100 g of toluene to form a homogeneous solution. The solutionwas formed into a film of 0.1 mm thickness by the casting method.

The so formed film was subjected to irradiation of a 400 watt highpressure mercury lamp disposed 15 cm apart from the sample film. Afterthe film had been exposed under irradiation for 32 hours, the degree ofpolymerization of the film was determined to be 650.

EXAMPLE 6

In the same manner as in Example 1, there was prepared astyrene-butadiene copolymer having a butadiene content of 4.87 % byweight and an average degree of polymerization of 1070.

Then, 5 g of the so prepared styrene-butadiene copolymer and 5 g ofpolystyrene having an average degree of polymerization of 1130 wereadded to 100 g of toluene to form a homogeneous solution. The solutionwas formed into a film of 0.1 mm thickness by the casting method.

The so formed film was subjected to irradiation of a 400 watt highpressure mercury lamp disposed 15 cm apart from the sample film. After32 hours' irradiation the degree of polymerization of the film wasdetermined to be 454.

EXAMPLE 7

In the same manner as in Example 2, there was prepared a styreneisoprenecopolymer having an isoprene content of 3.5 % by weight and an averagedegree of polymerization of 1310.

Then, 8 g of the so prepared copolymer and 2 g of polystyrene having anaverage degree of polymerization of 1130 were added to 100 g of tolueneto form a homogeneous solution. The solution was formed into a film of0.1 mm thickness by the casting method.

The film was subjected to irradiation of a 400 watt high pressuremercury lamp disposed 15 cm apart from the sample film. After 32 hours'irradiation, the degree of polymerization was determined to be 380.

EXAMPLE 8

Copolymers of Runs Nos. 19, 20 and 21 prepared in Example 4 (9 g each)were respectively blended with 1 g of poly(methyl methacrylate) of RunNo. 22, and each of the blends was dissolved in 100 g of toluene,respectively. Films of 0.1 mm thickness were prepared from the so formedhomogeneous solutions by the casting method. These films were subjectedto irradiation of a 400 watt high pressure mercury lamp disposed 15 cmapart from the sample film. After the irradiation had been continued fora predetermined period of time, the degree of polymerization wasdetermined. Results are shown in Table 5.

                                      Table 5                                     __________________________________________________________________________                               Degree of Polymerization                                          Poly(methyl      after 20                                                                            after 50                                Copolymer      methacrylate)                                                                             before                                                                             hours'                                                                              hours'                                  Run       Content     Content                                                                            irradia-                                                                           irradia-                                                                            irradia-                                No.                                                                              Kind   (wt. %)                                                                            Kind   (wt. %)                                                                            tion tion  tion                                    __________________________________________________________________________    23 product of                                                                           90   product of                                                                           10   1540 780   510                                        Run No. 19  Run No. 22                                                     24 product of                                                                           90   product of                                                                           10   1680 860   480                                        Run No. 20  Run No. 22                                                     25 product of                                                                           90   product of                                                                           10   1980 590   410                                        Run No. 21  Run No. 22                                                     __________________________________________________________________________

EXAMPLE 9

500 Grams of beads of a styrene-butadiene copolymer having a butadienecontent of 1.9 % by weight and a degree of polymerization of about 1150were taken into a 2-liter capacity autoclave charged with 700 g of a 0.5% aqueous solution of polyvinyl alcohol, and the temperature waselevated to 50°C. under agitation. Butane gas was introduced underpressure into the autoclave, and the temperature was maintained at 50°C.for 5 hours, following which the temperature was lowered. The resultingreaction product was taken out of the autoclave, washed with water,dried, and maintained at 10°C. for 3 days. Thus there were obtainedfoamable beads containing butane gas. The foamable beads were molded bymeans of an extruder to obtain a foamed sheet of 1.5 mm thickness havinga foam ratio of about 10,

When the sheet was left outdoors for 14 days, it was deteriorated tosuch an extent that it was crumbled away to powder only by picking itwith fingers. At that time the degree of polymerization of the sheet wasabout 500.

EXAMPLE 10

Foamable copolymer beads impregnated with butane gas were prepared inthe same manner as in Example 9 by employing a styrene-isoprenecopolymer having an isoprene content of 4.8 % by weight and a degree ofpolymerization of 2340.

The so prepared beads were taken into a mold and heated by steam toobtain a foamed article having an apparent density of 0.015. A sheet of15 mm thickness was cut from the so obtained foamed article, andsubjected for 100 hours to irradiation of a 400 watt high pressuremercury lamp disposed 30 cm apart from the sample sheet. As a result,the portion of the sheet from the irradiated surface to the interior ofa depth of about 5 mm became very fragile and was crumbled away intopowder only by touching it with finger tips.

For comparison, a polystyrene foamed sheet of 15 mm thickness preparedin the same manner as above from beads of polystyrene having a degree ofpolymerization of about 1500 was tested in the same manner as above. Inthis case, such extreme deterioration as described above was not causedto occur but only the surface portion of the sheet was discolored into afaintly yellow color.

EXAMPLE 11

Foamable copolymer beads impregnated with n-hexane were prepared in thesame manner as in Example 9 by employing a methyl methacrylate-butadienecopolymer having a butadiene content of 3.8 % by weight and a degree ofpolymerization of 3680. The so prepared foamable beads were taken into amold and heated by steam to obtain a foamed article having an apparentdensity of 0.018. A sheet of 15 mm thickness was cut from the foamedarticle, and when the sheet was left outdoors for 2 months, the sheetwas so deteriorated that the portion of the sheet from the surface tothe interior of a depth of about 3 mm was crumbled away into powder onlyby touching it with the finger tips.

For comparison, a foamed sheet of an apparent density of 0.018 preparedfrom poly(methyl methacrylate) having a degree of polymerization of 3240was left outdoors for 2 months in the same manner as above. However, thesurface portion of the sheet was hardly changed and it was not crumbledaway into powder by touching it with finger tips.

EXAMPLE 12

A mixture of 6 g of a copolymer of an average degree of polymerizationof 3240 composed of 95.8 % by weight of methyl methacrylate, 2.2 % byweight of butadiene and 2 % by weight of methyl vinyl ketone andprepared in the same manner as described in Example 4, with 4 g of poly(vinyl chloride) having an average degree of polymerization of 1100 wasdissolved in tetrahydrofuran, and the solution was formed into a film of0.1 mm thickness by the casting method. The so formed film was subjectedfor 85 hours to irradiation of a 400 watt high pressure mercury lampdisposed 30 cm apart from the sample film. The film was very fragile,and when a bending force was imposed on the film, it was broken away.

In the same manner as above, a film of 0.1 mm thickness was preparedfrom a mixture of 6 g of poly(methyl methacrylate) having an averagedegree of polymerization of 3240 and 4 g of poly(vinyl chloride) havingan average degree of polymerization of 1100, and the film was tested inthe same manner as above. In order for this film to show deteriorationsimilar to that of the above film formed according to this invention,the irradiation had to be conducted for more than 200 hours.

What we claim is:
 1. A photo-degradable non-rubbery resinous composition which comprises a blend of:a. from 50 to less than 100 % by weight of a copolymer composed of (i) 95.0 - 99.9 % by weight of a monomer selected from the group consisting of styrene and methyl methacrylate, (ii) 5.0 - 0.1 % by weight of a diene monomer and (iii) 0.5 to 4.9 % by weight of an unsaturated ketone having the formula ##EQU4## wherein R₁, R₂ and R₃, which may be the same or different, represent a hydrogen atom or a methy or phenyl group, the sum of the proportions of the monomers (i), (ii) and (iii) being 100% by weight and the sum of the weight percent of the diene monomer and the unsaturated ketone being not greater than 5% by weight, and b. greater than 0% by weight and up to 50 % by weight of a thermoplastic synthetic resin other than said copolymer, said thermoplastic synthetic resin being selected from the group consisting of polystyrene, polyethylene, polymethyl methacrylate and polyvinyl chloride.
 2. A photo-degradable resinous composition as set form in claim 1, wherein said diene is butadiene.
 3. A photo-degradable resinous composition as set forth in claim 1, wherein said diene is isoprene.
 4. A photo-degradable resinous composition as set forth in claim 1, wherein said unsaturated ketone is selected from the group consisting of methyl vinyl ketone, phenyl vinyl ketone, phenyl propenyl ketone and benzalacetophenone.
 5. A photo-degradable resinous composition as set forth in claim 1, which further comprises a foaming agent.
 6. A shaped article prepared by employing a photo-degradable resinous composition as set forth in claim
 1. 7. A shaped article as set forth in claim 6, which is a foam.
 8. A shaped article as set forth in claim 6, which is a film, sheet or container.
 9. A photo-degradable resinous composition as set forth in claim 1, wherein the diene monomer is selected from the group consisting of butadiene, isoprene, chloroprene, 2,3-dichlorobutadiene and 2,3-dimethylbutadiene.
 10. A photo-degradable resinous composition as set forth in claim 1, wherein the thermoplastic synthetic resin is blended in an amount of less than 30% by weight based on the weight of the composition. 